1. Field of the Invention
The present invention relates to a liquid crystal display device, more particularly, to a liquid crystal display panel in which blur due to ionic impurities generated during the sealing process is avoided.
2. Background of the Related Art
In general, the liquid crystal display (LCD) panel comprises upper and lower glass substrates with liquid crystal sealed in between the upper and lower glass substrates.
The lower glass substrate has a plurality of gate lines arranged in one direction with a certain distance between them and data lines arranged along another direction perpendicular to said gate lines with a certain distance between them to define rectangular pixel areas arranged in a matrix. Each of the pixel areas includes a thin film transistor (TFT) which has a gate electrode connected to one of the gate lines, a source electrode connected to one of the data lines, and a drain electrode connected to one of the pixel electrodes.
The upper glass substrate has a black matrix, a color filter layer and common electrode formed thereon.
The lower glass substrate and the upper glass substrate, as described above, are attached, leaving a space between the substrates, using a sealing material (sealant) in a seal pattern along the periphery of the substrates. Liquid crystal is then injected into the space between the upper and lower glass substrates.
A seal pattern of related art used for sealing the upper and lower glass substrates together will be described in reference to the FIGS. 1, 2 and 3.
FIG. 1 is a plan view of a seal pattern in a sealing area between upper and lower transparent substrates of the related art. FIG. 2 is a magnification of a part B in FIG. 1, and FIG. 3 is a partial sectional view of part C in FIG. 1.
As described above, the lower substrate 2 having signal lines (not shown), pixel electrodes 3 and TFTs (not shown) is attached to the upper substrate 1 having a black matrix (not shown), a color filter layer (not shown) and common electrode 4. The lower substrate 2 is spaced a predetermined distance from the upper substrate 1 by a seal pattern S. Liquid crystal is injected into an active area A of the LCD and then the area where the liquid crystal was injected is sealed by a sealing agent E, as shown in FIG. 1.
In other words, the upper and lower glass substrates are put together after printing the seal pattern S in an outline portion of the active area of the upper or lower glass substrate by a silk screen printing through a seal mask, and then liquid crystal is injected through an injection hole, which is followed by sealing the injection hole with the sealing agent E.
The corner portions of the seal pattern S are substantially a perpendicular rectangular shape as shown in FIG. 2.
The seal pattern of the related art LCD has the following problems:
First, impurity ions existing on the surfaces of the substrates are carried by the surface of the liquid crystal in a capillary phenomenon when the liquid crystal is injected in between the substrates. Accordingly, the impurity ions (e−) are deposited at the corner portions of the display panel in relatively larger amounts. Such impurity ions (e−) are activated at a high temperature of about 50 degrees and generate blurs at the corner portions of an operating LCD.
Second, ionic impurities existing within the seal pattern can migrate into the liquid crystal causing electric field distortion and thus generating blur in the active area A of a LCD. In other words, when the electric field is applied between the common electrode 4 and the pixel electrode 3 to induce the liquid crystal to have a different alignment, the preexisting ionic impurities (e−) in the seal pattern can penetrate into the liquid crystal in the active area A. The ionic impurities (e−) can then be adsorbed into the surface of the common electrode 4 and function as resistance components, so that electric field distortion will take place and result in blur in the active area A.